4.0L OHV cranks but won't start - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 10-04-2016
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Icon9 4.0L OHV cranks but won't start

Well people, this is the first time I've had any kind of reliability issue with my Ranger's engine. 1990 XLT ext cab 2x4 /auto. I bought it brand new. It now has 270,000 miles. Im not very savvy with fuel injected engines.
Here is my problem. The Ranger will crank just fine but will not start. I hooked up my inline spark tester. I have fire at the plugs. My buddy brought his fuel pressure gauge over. Fuel pressure at the rail is fine. I took the air intake hose off and shot starting fluid in the throttle body and it started right up then died. I'm thinking the injectors are not cycling, but am unclear on where they get their signal to fire from. Is that the crank sensor? If anyone could help, id appreciate it. thanks!
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Old 10-04-2016
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The fuel injectors should get their pulse control from a computer somewhere. I'm not too awful familiar with anything pre-96, but I would think fuel injection's principle is the same for the most part.

If I'm correct, it is possible that the computer is toasted. Are you able to obtain any flash codes? That would also be controlled by the computer. If you can, then it's reasonable to assume the computer is O.K.
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Old 10-04-2016
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1994 and earlier 4.0l Rangers use an EDIS-6 module for spark.
The CKP(crank position) sensor connects to the EDIS-6 module
EDIS-6 connects to coil pack.

It is a separate spark system, 1995 and up used newer computer and it runs spark.

The EDIS-6 module does send the CKP sensor timing to the computer(EEC/ECU/PCM), so computer can time the fuel injectors.
If CKP sensor had a problem then No Spark, along with no fuel injectors.
So CKP, EDIS and coil pack are OK if engine starts by adding fuel manually.

So problem will be in the wiring between EDIS module and computer, Computer itself or the wiring at the fuel injectors
Is the computer starting up?
Does the CEL(check engine light) come on when key is turned on?

Do you hear the fuel pump come on for 2 seconds when key is turned on?
Computer runs the fuel pump.

If CEL comes on and fuel pump runs for 2 seconds then computer is probably OK.

When you turn on the key all the fuel injectors should get 12volts, there is a Red wire that just daisy chains from one injector to the next that should have 12volts when ever key is on.
Test for voltage at fuel injectors

The computer GROUNDS the injectors to open them.
'94 and earlier will use Batch Fire fuel injection, on a V6 this means that the computer GROUNDS 3 fuel injectors at the same time to open them.
So there will be TWO ground wires coming from the computer, a White wire and a Tan wire, each wire will connect to 3 separate injectors.

Diagram here of the injector wiring and also the EDIS wiring to computer: http://www.therangerstation.com/tech...0_3_0_2of3.JPG
The EDIS is where the timing pulse comes from to open the injectors.

Both Ground wires failing at the same time would be very very long odds.
Red power wire could be damaged, which would stop all injectors.

Timing pulse wire from EDIS could be bad.

Computer has a 60-pin connector, if there was water intrusion then that could effect specific systems.
Good look here at your computer and wiring: Ford EEC-IV
Pin 56 is the PIP, the CKP pulse from EDIS module, that tells computer that Crank is turning and times the fuel injectors


You can open it, warranty is long over, lol, and make sure circuit board is OK, not damaged


One long shot and only ever read about it happening one time, bad TPS(throttle position sensor)
The computer has a Clear Flooded Engine Routine, this shuts off fuel injectors while cranking the engine to dry it out, spark stays on.
The TPS gets 5volts from computer, TPS sends back .6 to .9volts if throttle is closed
As gas pedal is pushed down throttle plate opens the TPS voltage will increase, at wide open throttle(WOT) the voltage back to computer will be above 4.5volts.

To start Clear Flooded Engine Routine, you turn the key on and press gas pedal to the floor, so computer is seeing above 4.5volts from TPS but no CKP pulse, engine off.
Computer won't ground injectors now, so no fuel.
Computer will start fuel injectors as soon as TPS voltage drops below 4.5volts.

If there was a short in the TPS or its wiring then computer could be "seeing" above 4.5volts any time key is on, so no fuel injectors.
Unplug TPS and try to start engine
Test TPS wires, key on, only 1 should have 5volts

Last edited by RonD; 10-04-2016 at 12:02 PM.
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Old 10-04-2016
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Wow, good info! Ill get to checking it out. Thank you for putting in the time to reply. Not only does it help me know where to go, but with a comprehensive answer like that this dummy just may learn something! lol.
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Old 10-04-2016
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update

Ok, so Here is what I figured out so far on my Ranger...

The CEL does not come on when I turn on the key on.
I can't hear the fuel pump come on for the two seconds when I turn the key.
I have no voltage at the fuel injectors.
I removed the computer to test pin 56 and figured I'd crack it open while it was out for a visual inspection. The clear coating on the board looked like it had been hot enough to boil, but there was no discoloration to the board. Just a bunch of tiny bubbles. I went ahead and ordered a computer while I check the rest of the wiring and pins in the computer harness. I don't want to fry a computer because I didn't check for proper voltage going into it. I have not tested pin 56 yet, probably won't get to that until tomorrow. Sound like I'm on the right track?
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Old 10-04-2016
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With no power to computer and fuel injectors with key on it could just be a blown fuse or bad relay.

Look here: What goes where in a fuse box on a 1990 ford ranger

There is a diagram of engine fuse box, EEC 30amp fuse is the one to check.

There is also an EEC Relay, could be under that fuse box or on the fender with 1 or 2 other relays.
Brown base relay is the EEC relay, Green base is Fuel Pump relay, Black base is WOT relay(optional)

When you turn on the key the ignition switch(under steering column), sends power to vehicle systems, one of those is the EEC relay.
EEC relay closes and sends that 30amp fuse power to computer(EEC), fuel pump relay, spark system, and fuel injectors.

So check it
If you pull out the relay from it's base, with key off, one slot should have 12volts, thats from the 30amp fuse.
With key on a 2nd slot should now have 12volts, thats from the ignition switch
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Old 10-04-2016
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Very good, Ron! I can't wait to check this stuff tomorrow. Thanks again.
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Old 10-05-2016
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Ron D. You are the man. After checking more connections, I found that my 30 amp Maxi-fuse to the ECM was blown! I pulled it twice and looked at it and couldn't see anything wrong. I put my meter on it and it said it was bad. $5.99 got me back on the road! Thank you very much for your expert guidance and knowledge!!!!
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Old 10-05-2016
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Good work !

Thanks for posting the fix
And especially the part about testing the fuse, I have wasted more than a few hours chasing a problem that was a bad fuse that "looked" OK
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Old 10-05-2016
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Awesome; gotta love cheap fixes.
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